Environmental Forensic Investigation in the Residential Neighborhood Volta Grande IV, Volta Redonda, RJ, Brazil, Using TPH and PAHs Analyses in Soil Samples

Abstract

This article presents the results of a forensic investigation concerning the origin of hydrocarbons detected in the subsurface soil of the residential neighborhood Volta Grande IV, Volta Redonda, RJ, Brazil Before the establishment of the residential neighborhood (between 1978 and 1993), a blend of steel slag with by-products of carbon-chemical origin neutralized with calcium carbonate was buried in a portion of the area. Part of this material remained in the site and was covered by clayey soil. The area was leveled, and the houses were then built. Previous studies detected the presence of hydrocarbons in the soil, especially Polycyclic Aromatic Hydrocarbons (PAHs) above the Brazilian regulatory standards of CONAMA 420/2009 (CONAMA, 2009). Concern was raised that these hydrocarbons might be derived from local steel mill wastes. CSN conducted a geoforensic investigation to delineate the location of the waste from the steelworks company, in which integrated forensic hydrocarbons fingerprinting and data interpretation techniques were used to characterize the chemical compositions. There is an increasing trend of employing environmental chemistry techniques to determine the source(s) and fate of the contaminants and, in some cases, to determine their age or each source’s share. Environmental forensic techniques and databases were originally developed in the oil industry and were initially applied to environmental work with the Exxon Valdez incident (Emsbo-Mattingly, and Litman, 2016; Morrison, 2000; Morrison et al, 2006; Wang and Fingas, 2003; Douglas, 2007). Since then, the techniques have been refined for identification of both petrogenic and pyrogenic materials. Chemical fingerprinting and diagnostic source ratios helped compare the hydrocarbon patterns of residential soils with regional background, soils with suspected steel mill residues (dark soil), and selected reference samples. The application of geoforensic techniques is recent and rare in Brazil. For this reason, this work also aims to contribute with the development and application of the geoforensic tools in Brazil. Soil samples were analyzed for TPH, TPH fingerprint (modified EPA 8015D method), PAHs and biomarkers (modified EPA 8270D method). The forensic investigation determined that the VOCs in the residential soil are associated with gasoline and possibly diesel fuel oil releases into the subsurface soils that are not associated with the steel mill waste. The PAHs in residential subsurface soil generally fell below background concentrations and are likely associated with regional soot. The PAHs in the three samples with concentrations above background (out of a total of thirty-six samples) exhibit compositional features similar to coal byproducts, such as tar and coke, possibly attributable to the steel mill operation. Soil from the eastern portion of the neighborhood contained chemical signatures similar to coal tar; signatures from other samples were comparable to degraded asphalt and urban soot. Residues were limited to approximately 10% of the area, between 1 and 3m of depth.